“Factor of mischief were found in the investigation,” Amar Singh said, “police successfully identified several individuals in the videos, and a total of seven were arrested,” Xinhua news agency quoted him as saying.

The suspects are believed to have quarrels with the residents at the religious school and might have started the fire in retribution, Amar Singh said, declining to provide more details on how it was committed.

All seven suspects were not attending schools, six tested positive to drugs while two have criminal records, he added.

A total of 21 students aged 6 to 17 and two teachers were killed in the early morning fire on Thursday near downtown Kuala Lumpur. Investigation by fire department showed that the fire was not started by short circuit as suspected earlier.